Field of the Invention
The present invention relates to a method for adjusting a recording head, and an image forming apparatus, and more particularly to a technique of adjusting discharge timing of an adjacent head module in a recording head formed by joining a plurality of head modules each of which is provided with a plurality of nozzles for discharging droplets.
Description of the Related Art
There is known a form using a line head formed by joining a plurality of head modules, as a recording head of an ink jet recorder as a form of an image forming apparatus. Japanese Patent Application Laid-Open No. 2014-136319 (Patent Literature 1) discloses a method of calculating a shift amount of an initial recording position in a Y-direction between a first head module and a second head module adjacent to each other. The Y-direction is a direction parallel to a paper sheet feeding direction.
In Patent Literature 1, a plurality of test patterns each with a different shift amount is recorded while a shift amount of a recording position in the Y-direction between the first head module and the second head module is changed, and concentration of a portion recorded by a recording element in a complementary region of the first head module and the second head module is acquired from readout data on the test patterns, and then a shift amount of an initial recording position in the Y-direction between the first head module and the second head module is calculated from a relationship between a shift amount and concentration. The “first head module” and the “second head module” in Patent Literature 1 are terms corresponding to a “first head module” and a “second head module” of the present specification, respectively.
Japanese Patent Application Laid-Open No. 2004-268452 (Patent Literature 2) describes a technique in which a shift amount of a printed letter between unit recording heads and that between recording heads in a paper sheet feeding direction is detected by reading an image for alignment adjustment to control ink injection timing so that a shift amount of a printed letter decreases. The “unit recording head” in Patent Literature 2 is a term corresponding to the “head module” of the present specification. The “shift amount of a printed letter” in Patent Literature 2 is a term corresponding to a “recording shift amount” in the present specification. The “ink injection timing” in Patent Literature 2 is a term corresponding to “discharge timing” of the present specification.
In addition, Japanese Patent Application Laid-Open No. 2011-168023 (Patent Literature 3) describes a technique in which drive timing is adjusted by outputting a predetermined test pattern to adjust a relative deposit position error being an amount of a level difference between sub heads by using an external reading device in a recording head formed by joining two or more sub heads. The “sub head” in Patent Literature 3 is a term corresponding to the “head module” of the present specification. The “relative deposit position error” in Patent Literature 3 is a term corresponding to the “recording shift amount” in the present specification. The “drive timing” in Patent Literature 3 is a term corresponding to the “discharge timing” of the present specification.